1. Field of the Invention
The present invention relates to a radio resource control method of controlling a radio resource for transmitting user data by a mobile station via an uplink, a radio base station, and a radio network controller.
2. Description of the Related Art
In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data is generated as shown in FIG. 2 (a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2(b), or, as shown in FIG. 2(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2(b) and 2(c).
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Under the 3GPP standards, cells transmit grants of uplink resources to mobile stations. At any given time, each mobile station has one “serving cell” in a radio base station from which the mobile station receives “Absolute Grants” via AGCH. The Absolute Grant provides an absolute limitation on the maximum amount uplink resources that the mobile station UE may use.
A mobile station UE may also receive “Relative Grants” that increase or decrease the resource limitation compared to the previously used value. A mobile station may receive the Relative Grants via RGCH not only from its serving cell but also from non-serving cells.
A cell in a radio base station Node B regards a mobile station for which the cell is a serving cell as a serving mobile station. A radio link (E-DCH) established between the mobile station and the cell is called a serving radio link (a serving E-DCH).
On the other hand, a cell in a radio base station Node B regards a mobile station for which the cell is a non-serving cell as a non-serving mobile station. A radio link (E-DCH) established between the mobile station and the cell is called a non-serving radio link (a non-serving E-DCH).
Radio resource control methods that have been discussed in the “Enhanced Uplink” can be broadly categorized into three as follows. The radio resource control methods will be briefly described below.
First, a radio resource control method that is referred to as “Time & Rate Control” has been discussed.
In such a radio resource control method, a radio base station Node B determines a mobile station UE which can transmit user data and a transmission rate of user data per a predetermined timing, so as to signal information relating to a mobile station ID as well as the transmission rate of user data (or a maximum allowable transmission rate of user data).
The mobile station UE that is designated by the radio base station Node B transmits user data at the predetermined timing and the transmission rate (or within a range of the maximum allowable transmission rate).
Second, a radio resource control method that is referred to as “Rate Control per UE” has been discussed.
In such a radio resource control method, if there is user data that should be transmitted to the radio base station Node B, each mobile station UE can transmit the user data. However, the maximum allowable transmission rate of the user data, which is determined by the radio base station Node B and signaled to each mobile station UE for each transmission frame or each of a plurality of transmission frames, is used.
Here, when the maximum allowable transmission rate is signaled, the radio base station Node B signals the maximum allowable transmission rate itself, or a relative value thereof (for example, binary of Up command and Down command), at this timing.
Third, a radio resource control method that is referred to as “Rate Control per Cell” has been discussed.
In such a radio resource control method, a radio base station Node B signals a transmission rate of user data, which is common among mobile stations UE in communication, or information needed to calculate the transmission rate, and each mobile station UE determines a transmission rate of user data based on the received information.
Although a downlink control signal load and a transmission rate control load in the radio base station Node B or the like exist, as proposed in “Time & Rate Control” and “Rate Control per UE”, to control the transmission rate of the each mobile station UE, respectively, can be a good control methods for improving radio capacity in an uplink.
The “Rate Control per UE” is configured to control the transmission rate of user data by using an “Absolute rate Grant Channel (AGCH)” and a “Relative rate Grant Channel (RGCH)”.
By using the RGCH frequently, it is possible to simplify the control signals transmitted from the radio base station Node B for controlling the transmission rate of user data, and to reduce effects in a downlink, which is caused by the control signals.
The detailed performance of the transmission rate control using the RGCH, which includes three values of an “Up command”, a “Down Command” and a “Hold Command”, is described in Non-Patent literature 1 (3GPP TSG-RAN R1-050002).
As described in the Non-Patent literature 1, the method that instructs to increase, decrease or hold the last transmission rate of HARQ is common.
Here, as disclosed in the Non-Patent literature 1, by using the concepts of hysteresis and window, the mobile station UE receiving the RGCH from a non-serving cell integrates the “Down Command” included in the received RGCH by tracing back for a predetermined period, and is specified to add such an integrated value to the transmission rate at the time (or, a parameter relating to the transmission rate, or “transmission power ratio between data channel and control cannel” in the Non-Patent literature 1).
As disclosed in the Non-Patent literature 1, the mobile station UE is provided with the hysteresis and the window so as to prevent “ping-pong phenomena” in which transmission of the “Up Command” from the serving cell and transmission of the “Down Command” from the non-serving cell are repeated.
In addition, the radio network controller RNC performs radio resource control so as to perform call admission control, handover control, or the like.
Conventionally, the radio network controller RNC performs the call admission control or the handover control based on the interference volume in the uplink.
However, when the EUL is applied, the interference volume in the uplink is constantly controlled so as to approach the allowable value.
Therefore, there is a problem that the call admission control or the handover control can not be performed simply based on the state whether or not the interference volume in the uplink has a space.
To solve these problems, there is known a method that the radio network control RNC measures received power of the EUL channel (Enhanced Dedicated Physical Channel) to perform the call admission control, the handover control, or the like, based on the measured received power.
However, in the conventional radio resource control method, there is a problem that the radio network controller RNC cannot correctly grasp the maximum allowable transmission rate reflecting the reduction range of the maximum allowable transmission rate signaled by the radio base station Node B, and high-performance radio resource control cannot be performed.